Emmanuel Genot

The Sherlock Holmes Sense of Revision

In the late 1980s, Merill B. and J. Hintikka proposed a reconstruction of the “Sherlock Holmes sense of deduction” (Hintikka & HIntikka, 1983, 1989). Before the Hintikkas, the consensus about Sherlock Holmes’ deductions, at least among philosophers and logicians who have considered the questions, had been that Holmes’ deductions were either enthymematic or ampliative. The Hintikkas argued that, appearances notwithstanding, Holmesian inferences were indeed ampliative, but that deduction played a strategic role in ampliation: Holmes draws conclusions by strengthening the premises he reasons from with answers to questions (ampliation) but select the questions based on the anticipation of the deductive consequences of their potential answers (deduction). An important aspect of the Hintikkas’ model was the idea that the source of answers can be thought of indifferently as external to the inquirer (Nature) or internal (Inquirer’s memory), as part of a naturalistic agenda.

After M.B. Hintikka’s demise, Hintikka went on to develop the logical foundations of the model which became the Interrogative Model of Inquiry (IMI). The naturalistic agenda was all but forgotten, as well as the relation between question-selection and memory. The formal results of the IMI focused on the relations between deduction simpliciter and deduction-cum-interrogation, and established in particular in which sense the role of deduction can be thought of as instrumental. Hintikka and his collaborators also discussed the relations between the IMI and other trends in formal epistemology, in particular nonmonotonic logics, and AGM belief revision theory, from a critical standpoint. They proposed an extension of their model and conjectured that it could be strengthened to offer an alternative to AGM revision and nomonotonic logics (Hintikka, Halonen & Mutanen, 1999).

The conjecture was later proved correct but with some qualifications: Hintikka’s method for handling nonmonotonic reasoning was provably related to well-known contraction operators that do not verify all the AGM axioms (Genot 2009, Genot 2011a). Hence, Hintikka’s misgivings were also by the same token proved partially ill-founded. However, these results did not respond to the main criticism addressed by Hintikka to AGM and non-AGM belief revision operators, namely that it collapses revision into a one-shot operation that presupposes a “fall-back theory”, whereas selecting candidates for revision is a also a strategic process (Genot, 2011b).

In this presentation, I will argue that the the key to understand this process is to look at it as an inquiry process that involves the inquirer’s memory and perception, not only for the purpose of choosing what to retain and what to cut out, but also what new information to take on board. I will support my argument with a recent re-evaluation of the Hintikkas’ program (Genot, 2017) and will illustrate it with one of the Hintikka’s favorite examples, Holmes’ reasoning in The Case of Silver Blaze (Hintikka & Hintikka 1989; Hintikka & Halonen, 2005; Genot & Jacot, 2012; Genot, 2017).



Genot (2009), The game of inquiry: the interrogative approach to inquiry and belief revision theory, Synthese, 171:271–289.
Genot (2011a), Incision by Bracketing: An Implementation of Kernel Contraction in Hintikka’s Tableaux System (Unpublished manuscript).

Genot (2011b), The Best of All Possible Worlds: Where Interrogative Games Meet Research Agendas, in E.J. Olsson, S. Enqvist (eds.), Belief Revision Meets Philosophy of Science, Springer.

Genot (2017), Strategies of inquiry: The ‘Sherlock Holmes sense of deduction’ revisited, Synthese, doi:10.1007/s11229-017-1319-x.

Genot & Gulz (2015), The Interrogative Model of Inquiry and Inquiry Learning, in C. Baskent (ed.), Perspectives on Interrogative Models of Inquiry, Springer.

Genot & Jacot (2012), How can yes-no questions be informative before they are answered? Strategic information in interrogative games, Episteme, 9:2 189–204.

Hintikka & Hintikka (1983), Sherlock Holmes confronts modern logic: Toward a theory of
information-seeking through questioning. In U. Eco & T. A. Sebeok (Eds.), The sign of three: Peirce, Dupin, Holmes. Bloomington: Indiana University Press.

Hintikka & Halonen (2005). Explanation: Retrospective reflections. Synthese, 143, 207–222.

Hintikka, Halonen & Mutanen (1999), Interrogative logic as a general theory of reasoning. In J. Hintikka, Inquiry as inquiry: A logic of scientific discovery. Dordrecht: Kluwer.